The amino acids can in turn be broken into various amines, some of which are reminiscent of ocean fish (trimethylamine), others of spoiling meat (putrescine); into strong sulfur compounds (a specialty of smear bacteria), or into simple ammonia, a powerful aroma that in overripened cheeses is harsh, like household cleaner.

They make fish inedible in a fraction of the time they take to spoil beef or pork, by consuming the savory free amino acids and then proteins and turning them into obnoxious nitrogen-containing substances (ammonia, trimethylamine, indole, skatole, putrescine, cadaverine) and sulfur compounds (hydrogen sulfide, skunky methanethiol).

Trimethylaminuria (TMAU), also known as fish malodor syndrome, is a rare metabolic disorder that prevents affected individuals from properly breaking down trimethylamine (TMA), instead letting it build up in the body.